The Bothnian Bay or Bay of Bothnia (; ) is the northernmost part of the Gulf of Bothnia, which is in turn the northern part of the Baltic Sea. The land holding the bay is still rising after the weight of ice-age glaciers has been removed, and within 2,000 years the bay will be a large freshwater lake since its link to the south Kvarken is mostly less than deep. The bay today is fed by several large rivers, and is relatively unaffected by tides, so has low salinity. It freezes each year for up to six months. Compared to other parts of the Baltic it has little plant or animal life. Extent The bay is divided from the Bothnian Sea, the southern part of the Gulf of Bothnia, by the Northern Quark (Kvarken) strait. The Northern Quark has a greatest depth of , with two ridges that are just deep. It lies between a group of islands off Vaasa in Finland and another group at Holmöarna in Sweden. The bay is bounded by Finland to the east and Sweden to the west. The bay is asymmetric, with a smoother and shallower bottom slope on the Finnish side, and a deeper bottom with a steeper and more rugged coast on the Swedish side. The Bothnian Bay has a catchment area of . Of this, 56% lies in Finland, 44% in Sweden and less than 1% in Norway. The catchment contains about of forest, split roughly equally between Sweden and Finland. The average depth is . The Luleå Deep is the deepest part of the bay, at , southeast of the town of Luleå. On the Finnish side the average depth is . The deepest part is near the island of Lönkytin, with a depth of . Isostatic rebound The bay lies in the area in Northern Europe where the ice was at its thickest during the last ice age. The Bay of Bothnia was under ice until the "Ancylus Lake" period (7500–6000 BC), when the ice sheet withdrew to the mountains of Northern Scandinavia. The land is now rising by post-glacial rebound at the highest rate in the Baltic Sea, at an estimated rate of a year. Today the Bothnian Bay lies around higher than it did at the end of the Ice age. The local population has seen the sea retreating during their lifetimes from piers and boathouses, leaving